When judging whether a character in a predetermined area surrounded by a line is correctly printed or not, a conventional method extracts the location of the line from density projection diagram of the predetermined area and then judges the location of the printed character according to the location of the line. When thin and short lines and characters are mixed on paper, however, it is difficult to extract the information on the line only. This means that there has been an obstacle to judging the state of the printed character in the area.